Hi.. Sometimes, when you dont know that you have number in childhood...start wearing glasses late..the eye may become weak or lazy ...so when given number also , it does not improve 100 %. Alternatively,  there could be some some irregular astigmatism, not correctable by glasses or some weakness in Retina too..which could cause this. For all practical purposes, this vision is good, unless someone is applying for jobs where 6/6 vision is mandatory.